Step two in an outbreak investigation is to describe the outbreak by person, place, and time. The key to all parts of an outbreak investigation is usually the line list. A line list provides a list of each individual case and their relevant characteristics. In this line list, for the previously described prairie dog monkeypox outbreak, we show the age of cases, their status based on our case definition. That is, whether they're a probable suspect or confirmed case. Information on their possible route of exposure, whether that's home, childcare facility, or elsewhere. The likely dates of exposure based on that possible exposure context, the date on which they had symptom onset, what their symptoms were. And the laboratory results that allow us to determine their case status. Using this line list, we can further characterize the outbreak by making an epidemic curve. In an epidemic curve, as the one shown here, we show the number of cases by the date of illness onset or some other metric of time. Here we further colored the cases by whether they're suspect, probable, or confirmed. Looking at the epidemic curve gives us a good characterization of the time course of the outbreak. Here showing we see our first probable cases on the 26th of May, most cases developed symptoms on the 29th of May, and we continue seeing cases until June 10th. The shape of an epidemic curve can further give us insight into what the cause of the outbreak is or what's driving the outbreak. So here we show an epidemic for a point source outbreak. So in a point source outbreak, everybody has been exposed at the same time or at the same event. For instance, this would classically occur if there was a food exposure at a lunch, or party, or something like that. So when we have a point source outbreak, we get an epidemic curve like this, where we have a quick increase in the number of cases, followed by a long and slow decrease, a long tail. For those of you familiar with it, this type of outbreak generally follows what's called a log-normal distribution or a long-tailed distribution, shown here in red. Another type of an outbreak is a common source outbreak. So this is a type of outbreak that might be driven by a continuous and ongoing exposure. For instance, if there was some environmental contaminant in the water that kept going, and going, and going over time, so people were continually exposed to it. So in this type of outbreak, there aren't really distinct patterns over time in the shape of an outbreak. We can think of it being a constant risk, here shown in red, over time, and we see similar numbers of cases on every day, with some random variation, regardless of when that occurs. The final type of outbreak is what we usually consider to be a outbreak. That is a propagated outbreak, where people are spreading the disease from one person to another over time, leading to a large epidemic. The epidemic curve here is typical of this type of outbreak. So first you'll notice we have a sort of bell-shaped curve with a slow increase in the number of cases, followed by a slow decrease in the number of cases. If you look closely, you can also see that there's waves of infection embedded in this outbreak. Here I've highlighted them by these red curves. So we see a small, little, mini outbreak at first. And then there's some time between when those cases occur and the cases they cause developed symptoms, and that causes another mini outbreak. And then there's some more time between when those cases occurred and when the people they infect develop symptoms, which causes another mini outbreak. And this process goes on and on, and these outbreaks slowly merge together, creating a large smooth curve over the entire course of the epidemic. So the epidemic curve characterizes the outbreak by time, but we also might want to characterize the outbreak by space. Mapping outbreaks is one of the oldest activities of epidemiology, and dates back at least to the time of John Snow, when he did his famous investigation of cholera at the Broad Street pump. Here I show a map that John Snow made during his investigation. And this is a point map, where we've put a point for each case based on where they occurred. Here this is each death due to cholera. And when John Snow put these points on this map, it was clear that the Broad Street pump, shown at the middle here, was in the center of the clouds of points. Providing evidence that this pump may be the source of the outbreak. Here is another map of the same epidemic, where the Broad Street pump is shown in red. Here John Snow made a bar graph for every address in the surrounding streets that showed how many cases occurred at that address. So you can see that by how on each street here, there's a black bar of a different height showing the number of cases occurring at that address during this outbreak. Looking at these, it becomes obvious that these cases are clustered around the Broad Street pump. We still use similar techniques that John Snow used back in the 1800s today when we investigate outbreaks. Here is a map of Ebola cases from the 2014 to 16 outbreak of Ebola that occurred in West Africa. It uses a combination of the dot map technique and the bar graph technique that John Snow used. Here individual dots show locations where Ebola occurred and shows the number of cases. Blue, showing the number of Ebola cases that have ever been confirmed in the area. And red, showing the number of recent Ebola cases. This gives us a sense of the spatial and temporal progression of the outbreak. So to summarize, a line list describes key characteristics of cases, including the time of symptom onset, clinical and epidemiological processes, and identifies these cases by person, place, and time. An epidemic curve describes the course of an outbreak over time. And the shape of this epidemic curve gives information about the source of the outbreak. Maps can also provide critical information about disease spread. As an exercise, look at this line list of cases and draw an epidemic curve for it. If you want, you can use the case definition you previously developed to further characterize the course of cases over time.